Recently changed my X1600pro for a HD3850 AGP card and notice a couple of issues.
ETQW with the same settings is actually a few FPS slower than on the X1600 which in turn was already about 5 FPS slower than the the windows driver. The FPS loss affects the minimum I see, so I now loose about 8 over windows when it most counts.
I don't have the fastest CPU - XP2500 running close to 3200 speeds, so this may be playing a part - but then on windows more demanding DirectX games like COD4 got quite a boost from the new card but ETQW didn't, so maybe OpenGL is a factor.
Older games are also a bit variable, the quake 3 demo timedemos may give 90fps one run but 70 the next. One time it almost ground to a halt, but I haven't reproduced that one yet. I noticed that it now always behaves as if I an running it with LIBGL_ALWAYS_INDIRECT=1 so it doesn't use compiled vertex arrays, which could be a factor. Other Q3 based gamed don't seem to be affected in the same way, but are not much faster than with the X1600.
Nexuix works fine and I get plenty of FPS at high settings.
Tested with 8.7, 8.6 and 8.4 (the download link for 8.5 was/is broken) 3D performaance with 8.4 is dire.
On all three drivers I have one minor issue with compiz fusion - when using <alt><tab> or <control><alt><down> the content of the windows doesn't display in the thumbnails. This worked OK on the X1600.
The content does display OK if I use the mouse top left/right of the screen to zoom out.